Transporting and classifying fluid solids



B. v. MOLSTEDT 2,959,284

Nov. 8, 1960 TRANSPORTING AND CLASSIFYING FLUID SOLIDS Filed June 28,1955 I2 FLUE GASES CONVERSION 1 PRODUCTS t II TRANSFER 3 LINE ,3; I6BURNER 37 l I I 1 [OJ cl-I4 T I a I: n

:5 CONVEYING i. l A 4 L) d 2 H 8 3a 5 VAPORIZABLE A MEDIUM 4- la 3CONVEYING as GAS COOL STEAM l 7 39 COARSE 5 souos lb v rELUTRIATORELUTRIATING FIGURE 1 1w--% GAS I 6 x COARSE FIGURE I 2o FIGURE III 4ELUTRIATION 24 GAS COARSE souos Inventor Byron V Molstedt B M /04, 4. 7-Attorney:

=Mided so d Unite Sta 'TRANSPORTING AN D CLASSIFYING FLUID SOLIDS ,Byron.Victor Molstedt, Baton Rouge, La., assignor to ,Esso Research,andEngineering Company, a corporati of' e awa :FiledJuneZS,1955,'Ser.No. 518,528

.3..Cla ims. .(Cl. 2tl9138) .,u se inanyprocesswherein it is desired totransport finely .t divided solids and to segregate the solids accordingto si z e,a nd/,or density. Typical of such processes are fluidcatalyticcracking processes, fluid, hydroforming processes with or,without shot circulation systems, shale oil recovery processes,gasification processes and combustion p oc ssesl lydrocarbon oil fluidcoking processes, generally well ,lcnown in the-art, are used toconvert'heavy residual oils ,byyyrolysis to coke and lighter distillatefractions. In one arrangement, the system comprises a reaction vessel or,cok ,er, ,and ,a heater orbnrner vessel. Fluid beds are usuallyemployed in both vessels but a transfer line humor or ireactor may alsobe used. In operation, a hea yoil is injected intothe coker containingfluidized .lrighternperaturecoke particles, at ca. 950 F., and ispartiallyvaporizcd and cracked. Product vapors are ,Ircrnoved overhead,and coke is continuously circulated to the bu nerland reheated bypartial combustion. Reference is made to US. 2,589,124 (Packie) whichillustrates one type of standpipe and riserfluid solids con- .veyingsystem, i,c., a U-seal, that may beused to circu- ,jla te thecokebetween vessels.

lnsnch a .cokinsp o e s, n y about 5 to of coke deposited on theoriginal solids is consumedin-the-burner to supply :heat. Consequently,the particles rcontinue tgtgrowin size because of the excess of cokeproduced. This growth ,in size causes fluidization and circulationdiificultiesunless measures are taken to prevent it. Normally excesscoke is withdrawn from the coking proc- -ess .as product to maintain theweight inventory of *the solids constant, and finelydivided seed coke isadded to maintain the'numerical inventory and size distribution ofsolidssubstantially uniform. It has been customary *in withdrawing the productcoke to classify it, as by elutriation, so that only relatively coarsecoke is withdrawn. This practice greatly reduces theamount ,ofseed colgethat must be supplied to-the system. ,A gas, e.g.,

steam, is used to ,e'fiect both circulation and elutriation t Qftholids.

This invention proposes a method and apparatus for concurrentlycirculating and classifying finely divided -solids, particularly fluidcoke particles used as -a heatcarrying medium .or contact solid inhydrocarbon oil .fluidcolging systems, whereby appreciable economies arees atent r 2,959,284 {Patented Nov. 8, 1960 rsecured-in the-consumptionof gases supplied to the process.

tmittingtfluidisolids to an, intermediate portion of said .yertioally..disposed. conduit, (conduit means for admitting an; e1utriating andconveyinggas. to said lower end por- .tion,. and;conduit means forwithdrawing relatively coarse ,solids from said lower end portion.

With specific reference .to Figure I, there is shown an.,elutriatorincorporated.into.a modified U-bend fluidized solids ,systemtransporting solids, e.g., coke particles, .betweenaafluid coker and atransfer line burner. The velutriation-circulation system of Figure I isparticularly applicable .to fluidized solids systems using low solids.aei ioulation .raf-eszandhigh gas rates, such as the transfer ,linesystem ;-shown-wherei n there may be a hightemperature;differencebetween the reaction and heating zones.

Figure .11 illustrates amore flexible system, ,i.e., a sys- 1ternwherein the .conditionsof elutriation can be changed without alteringmain process conditions.

,Referring, now to Figure I, .finelytdivided solids arewithdrawn.from-cokerlt) via standpipe 1a flowing down- .Wardlytherein.The standpipe is of=sufficientheight so that-thecolumn ,of aeratedsolids builds up .a hydrostatic ,pliosfiul'elsllfiicient to causecirculation of the solids around 'thebend of conduit 1 to anelutriatorfi. To decrease the density of the solids as they fiowupwardly in riser 112, additional amounts of an-aerating gas orconveying gas,

e. g., steam, can be admitted ,to conduit. 1 via;manifold systemi- Theelutr-iation zone in this .example comprises a substantiallyverticallyelongated conduit 3. The solids from .riser.;1b:are admittedtoanjntermediate portion of the elutriation zone. vSome of-the solidsi-so admitted fall downwardly into'the elutriation 'zoneand are met withanfilutriating gassupplied to the elutriation zone by line The velocityof elutriationgas in conduit 3 .is adjusted such that the desired amountof coarser solids .falldownwardly to the base of the elutriation zoneand .Ihoremainderof :the finer solids ,are conveyed upwardly..Thefioarser solids so segregated are removed from the .zoneby line .5.Distributingmeans 7 may be placed as shown within the elutriation zone.The distributing means may include perforated plates, screens, bars, or,rods. ,Insome-instances, it may be desirable to use rel-.Jatilelycoarse packingsuch as Raschig rings, the .use of Whichin suchamanneris well known in theart. The .gas admitted .by line 6 to theelutriation zone ;3 having accomplished the desired classifying actionpasses upwardly, ,mixes with the bulk of thesolids and conveying gas andserves to convey .the suspension upwardly vthrough outlet riser 4.Conduit4 merges into a transfer 'l ne burner wherein the coke particlesare partially "burned while being conveyed through the burner atvelocitiesabove1 O,ft./sec., e.g.,.60;ft./, sec.

lI'he elutriating gas applied to zone 3 can be inert with respect to.the solids or may be reactive therewith. It can 'alsobe a reactant usedin later processing steps. Thus, air can be supplied to zone 3 vialine-6 if the solids being handled are coke that is being passed to aburning system, as shown, or the gas may have desulfurizationcharacteristics, i.e., hydrogen may be used to eifect desulfurization offluid coke while it is being transferred. Additional amounts ofconveying gas or reactant gas such as air may be added to the solidssuspension via line 8 leaving the elutriation zone.

In other applications, conduit 4 may be used as a transfer line reactor.For example, methane may be admitted via line 8 to conduit 4 to contactthe heated solids and to thereby be decomposed into hydrogen and carbon.

In the process illustrated, the coke particles heated in the transferline burner are separated from the flue gases in cyclone system 11. Theflue gases are vented by line 12 and the heated coke particles aretransferred by line 13 to the coker 10. Steam is admitted by line 14 tothe base of vessel to fiuidize the solids therein. A heavy oil, e.g., aresidual oil, is injected into the coker by line 15 and upon contactwith the fluidized high temperature coke particles, undergoesvaporization and pyrolysis, depositing additional amounts of coke on thefluidized particles and evolving relatively lighter hydrocarbons; Thevapors are recovered overhead by line 16 as product after havingentrained solids removed.

While the invention is applicable to a wide range of solids having awide range in size and densities, it is particularly preferred toprocess solids having particle size ranges within the limits of about 0to 2000 microns. The density of the solid gas suspension in theelutriation zone below the point of a juncture of riser conduit 1b withthe elutriation zone is preferably within the range of 0.01 to 20lbs/cu. ft. when using solids having a true particle density in therange of to 300 lbs/cu. ft. This may conveniently be termed dispersephase elutriation.

In disperse phase elutriation, for the particle density and size rangeof particles identified, superficial gas velocities in the elutriationsection can vary from 0.1 to 50 ft. per second. Superficial gas velocityis the velocity of the gas passing up through the elutriator consideringthe elutriator as being empty.

Example A system as depicted in Figure I may have the followingdimensions: inlet conduit 1 10 ID. outlet conduit 4 13.2" I.D.,elutriation section 3 27" ID, 20 ft. long, with the inlet conduitjoining the elutriation section 12 ft. from the bottom. Three rows ofdistributing grids 3 ft. apart composed of A OD. bars on 1 /2" centersmay be located in the elutriation section. When handling fluid coke in asize range of approximately 10 to 1200 microns (about 190 microns medianparticle size) having a true particle density of 100 lbs./ft. 85,000lbs. of coke per hour as a steam-coke suspension having an inlet densityof 40 lbs/ft. and temperature of 950 F. at a pressure of 29 p.s.i.a. maybe admitted to the elutriation section via the inlet conduit. 94,000s.c.f. of steam per hour at a temperature of 335 F. and a pressure of110 p.s.i.a. are admitted to the base of the elutriation section toobtain a superficial gas velocity of 7.5 ft./sec. below the inletconduit, and 9 ft./sec. above the conduit. Under these conditions thematerial segregated will be predominantly larger than about 175-246microns. The segregated material will be removed from the main cokestream, and will be withdrawn from the elutriation section via line 5.In this design case, the material so withdrawn amounts to about 1.0 wt.percent of the coke charged to the elutriation section. The addedelutriation steam, plus the steam admitted to the zone via line 1,serves to convey upwardly through line 4 the remaining finer coke at avelocity of -40 ft. per second and a density of about 1.3 lbs/ft. at apressure of 29 p.s.i.a.

With reference to the above example, a more eflicient and more sharplydefined separation can be obtained by the use of various packings asmentioned previously and by re-adjustrnent of operating conditions as,for example, to a lower solids feed rate (or loading in lb.solids/s.c.f. gas) to the elutriation section. This adjustment isreadily accomplished by the apparatus shown in Figure II.

With reference to Figure II, some preferred modifications of theinvention will be described. Illustrated is a somewhat diflerentstandpipe 30 and riser 31 conduit system for circulating fluid solids.In this example, a valve 32 is used to regulate the flow of the solidsand to prevent backflow up standpipe 30. A conveying gas is admitted atthe base of the standpipe via line 33. This gas serves to convey thesolids by its jet effect and also by its dilution eifect upwardlythrough riser 31. Because the suspension in riser 31 is less dense thanthat of the aerated suspension in standpipe 30, a static driving forceis created as has been previously taught by the art. Elutriation zone 34is attached near the lower end portion of riser 31. The solids areadmitted to this elutriation zone from riser 31 via line 35. The use ofby-pass line 35 is a much preferred embodiment of this invention as itgives flexibility and control to the process. This by-pass line can alsobe used in conjunction with apparatus used in Figure I to regulate thequality and quantity of the classifying action, line 1b of Figure Iconnecting directly to line 4, and the by-pass line running between line1b and conduit 3.

In a fluid coking system, the temperature of the coke will normally beabove about 900 F. throughout the system. It is desirable, therefore, tocool the product coke in some manner before it is withdrawn in order toprevent spontaneous ignition of the coke upon contacting with theatmosphere. This is accomplished in the apparatus of Figure II bymaintaining a fluidized bed in the lower portion of elutriation zone 34and injecting a readily vaporizable medium into the fluidized bed vialine 36 which will effectively serve to cool the high temperature cokeand will create elutriating gas. This vaporizable medium may, forexample, comprise water, light naphthas or other oils. The vapors socreated pass upwardly through the elutriation zone classifying thesolids admitted to the zone by line 35 and carrying upwardly the finerportion of the solids to conduit 31. Of course, if this quenching actionis not desired, steam or other elutriating gas can be admitted to thebase of zone 34. Distributing means 38 may be used in zone 34 ifdesired. The elutriation gas then serves as a conveying gas in conduit31, conveying the suspension upwardly through the conduit. Additionalamounts of conveying gas may be added to conduit 31 as by conduit 37.The segregated coarse solids are removed from the base of zone 34 byline 39.

In some applications, it may be desirable to have the spent elutriationgas entering the riser system to enter as a high velocity jet by meansof a flow restricting means or nozzle. The jet serves to push the solidsupwardly through the conduit. This jet action may be accomplished, forexample, by restricting the outlet of the elutriation zone by a nipple40 as illustrated. Other types of orifices can, of course, be used. Thisinduced jet action is particularly efiicacious in the J-bend standpipeand riser system illustrated in Figure II. In other cases, it may bedesirable to inject some of the elutriation gas in such a fashion as toprovide extremely high velocity jets which will grind or break up someof the solids to fine particles, as in the case of producing seed cokefor fluid coking processes. These high velocity jets can be introducedin the dense bed of coarse solids collected in the base of theelutriation zone.

Another modification of the invention is shown in Figure III. There isillustrated a U-bend conduit system 20 transporting solids betweenreaction vessels. In this example, an inclined elutriator 21 is used toeffect classification of the solids. Th inclined elutriator is attachedto the lower end portion of the riser conduit of the U-bend system. Theelutriator 21 is inclined at an angle of from 160 from the verticalpreferably 30-60" and has preferably a flat or plane surface on thelower side of the inclination upon which descending solids may slide.Solids fall out of the riser conduit into th elutriation conduit andflow downwardly therein on the flat surface while being swept by anelutriation gas supplied to the elutriator via line 22. Instead of thecustomary dilute phase classifying action that occurs in verticalelutriators, countercurrent stripping action occurs with the fines beingremoved and conveyed upwardly from the surface of the sliding solids bythe action of the elutriation gas. The elutriation conduit 21 may be incascade or multiple arrangements and may have suitably placed baflies tobring about movement of solids within the sliding solids mass to causefines to be brought to the solids-gas interface.

For the previously described coke particles, it is preferred to operatewith coarse solidsproduct rates in the range of 100 to 15,000 lbs./hr./sq. ft, cross-section of the inclined elutriation conduit and with gasvelocities in the range of about 2-10 ft./sec. preferably from about 2to 6 ft./sec.

By the time the sliding solids mass reaches the lower end of elutriationconduit 21, the desired extent of classification has been obtained andthe coarse solids fall into reservoir 23. The coarse solids are thenremoved from the reservoir by line 24. The elutriation gas carrying theentrained finer solids passes from the upper end of the elutriationconduit 21 into the riser conduit and serves as conveying and dilutiongas therein.

Having described the invention, what is sought to be protected byLetters Patent is succinctly set forth in the following claims,

What is claimed is:

1. Apparatus for handling finely divided solids which includes avertically disposed conduit for upwardly transporting fluid solids, thelower end portion thereof being enlarged and adapted to classify solidsby elutriation, a riser conduit for upwardly admitting fluid solids toan intermediate portion of said vertically disposed conduit above saidenlarged portion, downwardly directed means leading from the bottominterior wall of said riser conduit for passing a portion of said fluidsolids from an intermediate portion of said riser conduit to said lower,enlarged end portion below the juncture of said riser conduit with saidvertically disposed conduit, conduit means for admitting an elutriatingand conveying gas to said lower enlarged end portion for elutriatingfine solids for upward passage through said vertically disposed conduit,and conduit means at the bottom of said enlarged lower end portion forwithdrawing relatively coarse solids from said lower enlarged endportion.

2. The apparatus of claim 1 which includes flow restricting means insaid vertically'disposed conduit immediately below the point of junctureof said riser conduit with said vertically disposed column whereby gasespassing upwardly from said flow restricting means into said verticallydisposed conduit thereabove have the characteristics of a jet.

3. A method for classifying by elutriation and circulating a stream offinely divided solids in a system of a size in the range of from 0 to2,000 microns while maintaining the flow of .the classified particles ofsaid stream in an upward direction substantially undisturbed, whichcomprises flowing said stream of finely divided solids from a fluidsolids zone through a downflow confined aerated column into an upwardlydirected less dense confined column, flowing elutriation gas upwardly ata velocity in the range of 0.1 to 50 ft./second through an elon gatedvertically arranged elutriation zone communicating at its upper end withsaid upwardly directed less dense column and having its lower portionenlarged, downwardly withdrawing a portion of the flowing solids streamfrom an intermediate portion of said upwardly directed less denseconfined column and passing withdrawn solids downwardly directly intosaid enlarged lower end portion, whereby relatively coarse solids falldownwardly into the lower portion of said elutriation zone collecting asa solids mass having an upper level substantially below the point ofadmission of the portion of said finely divided solids, removing saidrelatively coarse solids from said system, and continuing the flow ofsaid elutriation gas and the major portion of said stream of elutriatedfinely divided solids upwardly from said elutriation zone into saidupwardly directed less dense confined column, separating elutriatedsolids from said elutriation gas and returning said separated elutriatedsolids to said fluid solids zone.

References Cited in the file of this patent UNITED STATES PATENTS2,421,840 Lechthaler June 10, 1947 2,494,465 Watson et al. June 10, 19502,567,207 Hoge Sept. 11, 1951 2,589,124 Packie Mar. 11, 1952 2,621,034Stecker Dec. 9, 1952 2,661,324 Leifer Dec. 1, 1953 2,666,526 Odell eta1. Ian, 19, 1954 2,683,685 Matheson July 13, 1954 2,728,632 MathesonDec. 27, 1955 2,734,020 Brown Feb. 7, 1956 2,779,719 Spitz Jan. 29, 19572,796,391 Brown June 18, 1957

